Light sensitive device



jane. 2, 1934. s. RUBEN 1,941,494

LIGHT SENSITIVE DEVICE Filed June 30. 1950 4 Sheets-Shea?l l lIlII/llll jm 29 w34.

S. RUBEN LIGHT SENSITIVE DEVICE Filed June 30. 1930 A Sheets-Sheet 2 I I l l eno noo Time [n hours.-

Frequency 1h Cycles Jan. z, 1934. s, RUBEN 1,941,494

LIGHT SENSITIVE DEVICE Filed June 30. 1930 4 Sheets-Sheet 3 Jn. 2, 1934 s RUBEN LIGHT SENSITIVE DEVICE 4 Sheets-Sheet 4 Filed June so. 1930 [n0/yann Amis Patented Jan. 2; 1934 PATENT OFFICE ucm' SENSITIVE nEvIcE REISSUED' Samuel New Rochelle, N. Y.V appunti@ .Ime so, Isso. sei-In No. 464,838

This invention relates to devices which are electrically responsive to light variations.

This application is a continuation m part of my copending applications S. N. 301,884 filed 5 23 August 1928; S. N. 306,607 led 17 September 1928; S. N. 331,943 led 11 January 1929; S. N. 347,726 filed 16 March 1929; S. N. 412,077 led 6 December 1929 and S. N. 424,509 filed 30 Jannary 1930. l v

One of the objects of the invention is to provide a light-sensitive device which will respond uniformly to light variations throughout the visible range.

Another object of the invention is to provide a light-sensitive device which will operate without material electrolytic action.

Another object of the invention is to provide a light-sensitive device which will operate without material local chemical eects.

Still another object of the invention is to provide a light-sensitive cell which is adaptable to quantity production with uniform electril clniuacteristics.

Another object of rthe invention is'to provide a light-sensitive cell which has substantially no local chemical or electrolytic effects during nonuse thereof.

A further object of the invention is to provide a light-sensitive device which has a potential drop across the terminals thereof when the device is dark.

A still iin-ther object of the invention is to provide a light-sensitive device which may be connected in series or in parallel with an t im source of current supply without material electrolytic eects. due to dierent potentials.

Another object of the invention is to provide a light-sensitive device which is ww" in a circuit with a continuous iiow or current. o vStill another object oi the invention is to me vide a light-sensitive device having a low mis very simple, has few (Cl. 1H)

rials may be made to respond to high frequency light variationsif properly and used in the proper manner. I prefer to provide the lightsensitive material as a coating for an electrode which may be formed of a suitable base metal such as copper, and which may be potioned in a suitable container filled with a conducting medium insuchamannerastoreceivelightthrown upon it. A cooperating electrode formed oi a suitable metal, also depending somewhat on the light-sensitive material used. may be positioned 1n proximity to the light-sensitive electrode.

li have foimd hy careful experimentation that some of the factors which may aid in attaining theobjectsstatedahovemayheoutlinedasfo follows:

i. Tliebeseuponwhichthe light-cenaitivema terial is formed, coated, or otherwise attached may be some metal which is not particularly active with respect to the light-sensitive material thus avoiding the formation of compounds which mighttendtodeshoytheaensitivityoithe material.

2 Themetalservingasthecooperangelectrode for the light-sensitive material may be chosen sothatthereisaminimum diierenceo! potential hetween it and the .light-sensitive elecinode when mounted in the device. Thus chemicaleecisoreleehrolytic eectseitherinthe dark, or when not used, or where a conductive circuit is employed may he maintained at a 3. Where the conducting medium has the oualitsr of absorhine light a minimum of limi: may he ahsorhed hy placing the lightsensive electrode 55 uw 33 womit.: E30 th@ Wind' 0W @E Hgh@ mf alhe conductingmednmmaybenichthat it om not mix-m, dissolve the light-omsinve material to orm c. sInface product which might the light-sensinve -num may m mh @s ml l0@ Vy reen with medium may aim pretertaining the sensitive oon- :'ve surface.

in use and it may preferably have a high decomposition potential.

8. .A conducting medium having an acidic reaction or a tendency to form an acidic solution of a salt appears to be desirable.

9. Where a liquid conducting medium is used the concentration thereof may preferably be within certain denite limits because if too weak it may offer too high an impedance in the circuit and if too strong it might attack the lightsensitive surface and form a surface product thereon thereby destroying the light-sensitive quality thereof or it may produce a light absorbing compound in the conducting medium.

The invention has been illustrated in the accompanying drawings in which:

Fig. 1 is a sectional side elevation of a lightsensitive cell embodying the invention and showing the circuit connections therefor:

Fig. 2 is a sectional elevation through the light-sensitive element shown in Fig. 1;

Fig. 3 is a perspective view of the light-sensitive element shown in Fig. 1;

Fig. 4 is a graph showing the output difference between two different kinds of light-sensitive elements;

Fig. 5 is a pair of graphs illustrating the difference in life of the light-sensitive cell when connected in two different kinds of circuits;

Fig. 6 is a diagrammatic representation of a conductive circuit for the light-sensitive cell;

Fig. 7 is a circuit diagram illustrating a modified form of the circuit connection for the cell;

Fig. 8 is a wiring diagram of another modified form of the circuit for the cell;

Fig. 9 is a diagrammatical representation of a modified form of the cell functioning similar to the circuit of Fig. 8;

Figs. 10 and 11 are graphs showing the differenteffects of conducting mediums for the cell having acidic and basic reactions:

Fig. 12 is a series of graphs illustrating the l effect on the life of the cell of a number of difand Fig. 14 is a series of graphs illustrating the effects with the cell in a conductive circuit of a plurality of different metals for the cooperating electrodes.

In Fig. 1 I have shown a convenient type of light-sensitive'cell in which a casing 10 of suitable dielectric material such as bakelite may be provided with an opening 11 which is threaded on the inner side thereof to receive the threaded inwardly extending portion 12 of a rim 13. A glass lens or window 14 may be held in place by the rim 13 against a shoulder 15 formed on the inside of the opening 11. T he glass 14 has a liquid tight connection to prevent leakage of liquid if liquid is used as the conducting medium.

The light-sensitive element 16 may be mounted inside of the casing 10 by means of a headed pin 17 which passes through a foot 18 provided integral with the light-sensitive element. The pin 17 may be secured by a suitable nut 19 which may be threaded thereupon and brought tight against the lower outer wall of the casing which is flattened at that point, as indicated. to receive it. The cooperating electrode 20 may comprise a pin having a threaded portion 21 which may be threaded into a hole provided for that purpose in the casing wall at the base thereOf as indicated.

. The light sensitive surface is preferably formed from a copper base, such as is disclosed in my co-pending application S. N. 301,684 iled 23 August 1928 in which is shown a light sensitive electrode composed of copper having a thermally integrally formed cuprous oxide layer, a co-operating electrode such zinc or magnesiumand an electrolyte containing cobalt chloride. Thus the copper disc 25 (Fig. 2) which forms the electrode 16 is preferably electrolytic copper and may be formed with the foot 18 provided with a hole 27 to secure the electrode in position. The disc 25 may be heated in a furnace in air to approximately 1000 C. and for a period of time suiiicient to form a coating 28 of cuprous oxide of desired thickness on one side thereof. The furnace may then be turned off and the electrode may be allowed to cool down with the. furnace till it reaches room temperature. outer surface of the oxide may take on an extra atom of oxygen to the molecule so that it becomes cupric oxide instead of cuprous oxide and as cupric oxide does not appear to be as sensitive to light and is opaque I prefer to remove all traces of the cupric oxide by immersing the electrode ina bath of hydrochloric acid. After this treatment the electrode is preferably treated to remove the product of the hydrochloric acid reaction as for example by immersing it in concentrated nitric acid. 'Ihe nitric acid may then be removed by washing the electrode with distilled water. I have found that by etching the surface of the light-sensitive material to expose its crystalline structure it will respond to very much higher frequencies than when the surface is not etched and the difference between an etched and an unetched surface is indicated by the graphs shown in Fig. 4 where the differential potential of the cell, or the difference between dark and light potentials, is measured on the vertical axis while the number of cycles is measured on the horizontal axis. The unetched surface has'its maximum response under 100 cycles and falls off sharply to zero at slightly over 100 cycles while the etched surface maintains its maximum response up to a point in the neighborhood of 6000c cycles. The etching, which may be accomplished by immersing the electrode in a 10% solution of sulphuric acid, appears to not only increase the absorption surface or actual working area of the electrode but it seems to help prevent localized voltaic and photo-chemical effects. The etching preferably should be as uniform as possible in order to prevent inactive areas which reduce the sensitivity of the cell and perhaps cause local circuits which shorten the life thereof. When the etching has been completed a dense homogeneous layer of crystalline cuprous oxide is left on the surface of the copper disc and after the surface has been cleansed with distilled water and when all other portions of the disc have been covered by an insulating paint 29 such as asphaltum paint the electrode is ready to mount in the light-sensitive 1 cell.

A photo-sensitive electrode comprising a cop- The extreme per base having a thermally integrally formed cuprous oxide layer, chemically etched to expose the crystalline structure so as to give an eicient response to light modulations'of highspeed, is disclosed in my copending application S. N. 331,943 filed 11 January 1929. A similar etching is also shown in my co-pending application S. N. 412,077 filed 6 December 1929.'

The cooperating electrode 20 may be of any desired metal or compound as will be hereinafter described depending on the type of light-sensitive material used and the conducting medium.

In Fig. l the light-sensitive cell is shown connected in series with a condenser 30 and primary 31 of a transformer 32 the secondary 33 of which may be connected to the input of an amplifier (not shown) for suitably increasing the impulse produced by the light sensitive cell. In this capacity circuit the condenser 30 prevents' any direct current flow through the light-sensitive cell between the electrodes 16 and 20 and therefore any electrolytic or electro-chemical actions between the electrodes.

Figure 5 shows output curves in which, in one instance, the cell is directly or conductively coupled to the output transformer as shown in Fig. 6, as compared, in the other instance, to a cell which is coupled to the output transformer through a capacitance as shown in Fig. l.

The potential dierence of the cell is measured on the vertical axis and the time in hours is measured on the horizontal axis. It will be noted that in a conductive circuit the potential difference falls down practically to zero at the end of hours while in a capacitance circuit the um potential difference is maintained even beyond 1,000 hours. These figures are on a light-sensitive electrode having an of about 41 of a square inch and would be diiferent with electrodes of dierent areas.

InFigGthe primarywinding34lofatransformer 35 is shown connected directly across the terminals of the light-sensitive cell so that any potential diierence generated between the elements of the cell will cause current to dow in the circuit through the winding 3e and `therefore through the conducting medium between the light-sensitive elements and the cooperating element. With this circuit there may be a tendency for electrolytic action between the electrodes but suitable choice of a cooperating electrode as well as the conducting medium will keep such action to a In Mg. 'Z a circuit is shown which acts similarly to that-of Fig. l. In this case a uni-laterally conductive couple 3G, such as one composed of ajunction of magnesium 37 and cupric sulphide 3e, permits current to now in one direction only trom the magnesium toward the cupric sulphide, but if this is connected to the light-sensitive cell as indicated where the light-sensitive electrode is positive under the influence of light. no current can now in the circuit due to light modulations. The potential dierence will however be impressed across the transformer. due to the interelement capacities or the couple. Other couples might be used such as acopper-cuprous oxide couple.

Another means for preventing current from owing in the circuit is indicated in Fig. S where an electrolytic condenser may comprise a conrainer 39 provided .with a liquid such as a 5% solution of sulphuric acid and with a nlm-forming rod al such as tantalum inserted therein. The other electrode lla may be lead or any other metal which `svill not react with the solution. The lm formed on the tantalum wire acts to block a steady flow of current of high density but due to its inherent electrostatic capacity it will serve as an electrolytic condenser discharging pulsating currents. In Fig. 9 a diierent type of cell is shown in which the light-sensitive electrode 42 is cemented in the casing forming two compartments and is not directly connected to the output circuit but an additional electrode 43 of tantalum wire, similar to that shown in Fig. 8, is inserted in the liquid and prevents current from flowing between the electrodes except in one direction only which is opposite to the current which will be normally caused by the influence of light on the light-sensitive surface. The cooperating electrode 43a may be of copper as in the construction of Fig. l.

By experiment I have found that a conducting medium with a ,slightly acidic action is preferred for giving greater response to audio frequencies andfor giving a long life to the cell. If an acid solution of about one-half percent concentration is used for the conductive medium a cell with a cuprous oxide light-sensitive electrode such as shown in Fig. 1 will give excellent dynamic response. In my copending applications S. N. 412,077, filed 6 December 1929 and S. N. 424.509 led 30 January 1930, an electrolyte containing a weak solution of an organic acid such as citric, butyric or oxalic acid, is described. This response is indicated in Fig. l0 where a graph showing the percentage of concentration of the acid solution is measured along 100 the horizontal am's and the dilerential potential response is measured on the vertical axis.

As the acid is in up to one-half of one percent the potential of the cell increases to a mammum point giving good results and then if potassium hydrate is added slowly to neutralize the acid the potential difference falls oi as indicated in the curve until when the solution is substantially neutral it has reached a point so as to be barely perceptible. Y1

This differential potential represents the A: n response of the cell under inuence of modulated light at audio frequencies. When more potassium hydrate is added so as to give the solution a basic reaction there appears to be substantially no dilerential potential at all. In the case of the cuprous oxide light-sensitive material this would appear to, indicate that the contact potential difference of the omde is opposite in an alkaline solution to that when it is in an acid solution probably due to the hydrogen ion content o the electrolyte, or due perhaps to the asymmetrical characteristic of the cuprous omde layer on the copper electrode, for instance the uni-lateral conductivity thereof. and the current ow or nse to light is blocked. l an external source of potential is applied with its cathode connected to the cuprous oxide in a wwe solution a response can be obtained but with a short life due to electrolytic eects.

If after the output has fallen to zero more acid is added it may be caused to rise to the normal value again. l have checked this result by starting with a basic solution as indicated by the graph of lig. ll and adding lactic acid until the basic solution `was neut. At this point the output potential of the cell begins to rise and as the acid content is incre the output rises until it reaches its high point similar to that dy described in connection with Fig. l0. However as the acid is increased in the solution a point is reached when. it begins to attack the light-sensitive electrode. This causes the voltage output to decrease rather rapidly due to two elects: The first is probably due to the electro-physical effect on the light-sensitive surface reducing its sensitivity and the second to the fact that the product of the chemical action i5@ is distributed in the liquid conducting medium thereby increasing its light absorption.

In Fig. 12 where L represents relative life and C represents acidic concentration I have illustrated the etl'ect of a number of different acids upon the life of the cell by a series of curves where the vertical measurements represent life of the cell andthe horizontal concentration of the acid. As has been stated before when the acid becomes too strong it attacks the lightsensitive surface causing a diminution of the response thereof. From an inspection of the graphs it will be seen that an inorganic acid such as hydrochloric, nitric, sulphuric, hydrouoric, hydrobromic, hydroiodic, and phosphoric acid causes the life of the cell to fall oil by attacking the light-sensitive electrode at relatively low concentration of the acid. The organic acids permit a longer life with greater concentration and the following are indicated by the graphs in the order of their aiect upon the life of the cell: oxalic acid, formic acid, acetic acid, butyric acid, citric acid, and lactic acid, the latter appearing to permit the greatest concentration without attacking the light-sensitive material.

Other conductive solutions may be used if desired such as chlorides, iodides, iluorides, and bromides, of sodium, potassium, magnesium, beryllium, aluminum, strontium, rubdium, csium, lithium, and others including the chlorides of iron, nickel, and cobalt. All of these salt solutions appear to be operable in a conducting circuit such as is shown in Fig. 6 but vcobalt chloride is preferably the one operable in a capacitance circuit.

Fig. 13 shows'a graph similar to those of Figs. 10 and 11 but illustrating the operation of a cell with cobalt chloride. As the concentration of cobalt chloride increases a point is reached where the pink color of the cobalt chloride begins to absorb the light and thereby cut down the potential difference in the'cell. If the cobalt chloride is made basic by the addition of potassium hydrate the output potential drops down to zero as in the case illustrated in Figs. 10 and 11.

` Wherea capacitance circuit is used there appears to be very little dierence in the output of the cell when different metals are used for the cooperating electrode but when the cell is used in a conductive circuit the metal out of which the cooperating electrode is made appears to have considerable effect upon the output potential. Thus in Fig. 14 I have illustrated by means of a series of graphs the contact potential difference of cells having cuprous oxide light-sensitive surfaces used in a conductive circuit with different metals for the cooperating electrodes. In this gure it will be noted that the metals are indicated in the order of their potentials as follows: zinc, iron, lead, nickel and copper. From actual experiment the voltage output for these different metals was as follows:

When the cell is operating in a conductive circuit and with an electro-positive electrode, such as zinc, the operation of the cell is somewhat different than a capacitance circuit. In Such an arrangement the cell acts more like a valve,

for the zinc generates a large potential with respect to the light-sensitive material and the electrolyte used, but the current flow is regulated' due to the internal resistance change of the cell as governed by the change of contact potential of the light-sensitive surface and the electrolyte and the change of the internal resistance of the translucent and exposed light-sensitive surface. Thus the final potential generated by the cell is governed by that generated by the zinc electrode and particular electrolyte used. With lactic acid 0.98 of a volt was obtained when exposed to light and with hydrofluoric acid 1.08 volts was generated.

When photo-electric cells of this type are used in a circuit where current can flow between the two electrodes there is an electrolytic effect upon the electrodes with rapid destruction of the photosensitive surface. This ac tion is not purely photochemical as it occurs only when the circuit has been completed so that the photocell operates as a voltaic cell.

The life of a cell of this type appears to depend on the area of the photo-sensitive electrode and upon the potential difference between that electrode and the cooperating electrode. Thus with a cell having a zinc cooperating electrode the life is shorter than one having a nickel electrode.

Operation in a capacitance circuit is highly desirable because for eilicient operation in a conductive circuit with the external resistance equal to the cell resistance due to electrolytic effects with both dark and light current a cell with an area of one square inch of exposed surface may have a life of about 20 continuous hours. Where the cell so connected is allowed to stand without a load for periods of time the layer of cuprous oxide and copper that is formed may slowly dissolve into the electrolyte so that the cell is recuperated. The life of the cell will then depend on the number of recuperation periods and the lengths of these periods as compared with the lengths of the operating periods and both of the electrodes are slowly dissolved into the electrolyte. Another undesirable feature of depending upon the chemical restoration of the photo-sensitive electrode is that the product of the-action, at least where a cuprous oxide electrode is used, by the dissolution into the solution will color the electrolyte and greatly increase the absorption of light by the coloring compound in the electrolyte. By use of the capacitance coupling as indicated in Fig. 1 light-sensitive cells with cuprous oxide electrodes may be continuously operated for thousands of hours without showing a trace of electrolytic effects, reduction of sensitivity, or change in characteristics.

The use of capacitance coupling also prevents current flow and allows the cell to remain in the amplifier circuit without having to be electrically -fz disconected when not in use which is apparently necessary with the photo-voltaic cell or a cuprous oxide contact potential cell in a conducting circuit.

I have indicated above that acids may be used in the cell and also that certain salts may be used to advantage and I have discovered that in some instances a high output could.i be obtained without increasing the chemical attack on the cuprous oxide surface, where it is used, if instead of using solely an acid a combination of the acid and a salt of the acid, especially a copper salt, is used, for example a solution of lactic acid and cuprous lactate, or acetic acid and cuprous acetate, or citric acid and copper citrate, but in lll,

all these combinations I prefer to keep the salt content of the solution to a relatively low value as it tends to increase the absorption of light. The proper concentrations of acids, however, gives as good if not better results and eliminates light absorption to a large extent. The weak organic acids s uch as lactic, acetic, or citric acid, in the order named, give the longest life and the inorganic acids unless diluted to percentages less than one-half of one percent chemically aiect the life of the cell. In general the life is dependent upon the rate of attack of the acid on the light-sensitive material. This also applies to organic acids for if they are too strong, greater than two percent, they may chemically attack the electrode cutting down the life of the cell.

Where the cell is used in a capacitance circuit minimum electrolytic effects may be obtained by keeping the inherent potential of the cooperating electrode with the light-sensitive electrode as little electro-positive as possible and preferably slightly electronegative. This may be done by forming a sulphide on the surface of the cooperating electrode as by heating it in the present of sulphur atmosphere. In my co-pending application S. N. 347,726, led 16 March 1929, there is described a cell utilizing the thermally formed copper-cuprous oxide light sensitive electrode in combination With an electrode which is electro-negative with respect thereto, in order to reduce the polarization potential to a minimum. In my application S; N. 412,077, a cooperating copper sulphide electrode is described and used for the same purpose.

Those salts which tend to form basic solutions when electrolized give practically no response when in a capacitance circuit. The eiect of such salts is shownin the accompanying table:

'ses 4 I have found that one of the reasons why the output of a cell drops over a period of time, as has already been pointed out above, is the chemical attack of the electrolyte on the light-sensitive surface especially if a strong acid is used which produces a small amount of cuprous salt such as cuprous acetate having a blue coloring and therefore increasing the absorption of light. It is for this reason that I prefer a weak lactic acid electrolyte because it reacts to a minimum amount with the cuprous oxide electrode and the cooperating electrode. This action may be further minimized by using ethyleneglycol .or glycerine for .the acid diluting material instead of water. This will materially reduce the chemical effect and consequent cause of light absorption. This is also onel of the reasons why I prefer to plication S. N. 412,077 filed 6 December 1929, is

disclosed an electrolyte containing glycerine or ethyl glycol.

Certain metallic salts when dissociated may form acidic salts, as cobalt chloride which can dissociate into cobaltus acid.

A cell constructed in accordance with the principles as above described has a relatively low impedance which may be in the neighborhood of 1500 ohms.

Many modifications of the invention may be resorted to without departing from the spirit thereof and I do not therefore desire to limit the invention except as such limitations occur in the appended claims.

What I claim is:

l. A photo-voltaic cell having a container, a photo-sensitive electrode comprising a copper base having a thermally integrally formed etched crystalline cuprous oxide surface, a cooperating electrode and an electrolyte in contact with both electrodes.

2. A photo-voltaic cell as described in claim 1 in which the cooperating electrode is composed of copper.

3. A photo-voltaic cell as described in claim l in which the cooperating electrode is composed of zinc.

4. A photo-voltaic cell as described in claim 1 in which the cooperating electrode is composed of a material electro-negative with respect to said cuprous oxide.

5. A photo-voltaic cell having a'container, a photo-sensitive electrode comprising a copper base having a. thermally integrally formed etched crystalline cuprous oxide surface, a cooperating electrode and-an electrolyte containing an acid.

6. A photo-voltaic cell as described in claim 5 in which the electrolyte contains lactic acid.

7. A photo-voltaic cell having a container, a photo-sensitive electrode comprising a copper base having a thermally integrally formedetched crystalline cuprous oxide surface, a cooperating electrode and an electrolyte containing a haloid solution in contact with both electrodes.

8. A photo-voltaic cell as described in claim. '7 in which the cooperating electrode is composed of copper.

9. A photo-voltaic cell having a container, a pbotosensitive electrode comprising a copper base having a thermally integrally formed crystalline cuprous oxide surface, a cooperating electrode and an electrolyte containing cobalt chloride in contact with both electrodes.

SAMUEL RUBEN. 

